This is a competing continuation application that focuses on the biomechanical analysis of traumatic brain injury models. In the last project period, we identified the mechanical thresholds for vascular damage and traumatic axonal injury. Although significant, these primary neuropathological changes represent only a fraction of the events that occur during trauma. In this project period, our long term objective is determine the local mechanical stress conditions that distinguish apoptotic and necrotic cell death in vivo, and to measure the change in mechanical tolerance for both neuronal and apoptotic cell death across different brain regions. Our overlying hypothesis is that the mechanical threshold for apoptosis is below the necrotic cell death threshold, and that different mechanical thresholds exist for the cortex and hippocampus. We propose further that the proximal mechanisms for immediate shifts in cytosolic calcium caused at the threshold levels for apoptosis and necrosis by mechanical stretch are distinct. The specific aims of the research are as follows: (1) to measure the mechanical thresholds for in vivo neuronal apoptosis and necrosis using an in vivo model and finite element simulation, (2) to calculate the relative in vitro mechanical thresholds for apoptotic and necrotic changes in neurons across two brain regions - the cortex and the hippocampus, and (3) determine the mechanisms of calcium influx in neurons caused under the mechanical conditions of necrosis and apoptosis. By accomplishing the aims of the research plan, we expect to transfer 'mechanical stress maps' that describe the regional deformations of the brain that occur at the moment of injury to 'cellular response maps' that predict the areas of cellular changes occurring from the biomechanical forces during injury. Once accomplished, the research will significantly enhance the interpretation of existing models to understand a portion of the molecular sequelae and, in turn, treatment strategies for closed head injury.